To assess the functional performance, a further aim of the study is to develop a new test battery consisting of strength tests and single-leg hop tests with the ability to distinguish between the functional performance of the injured and the uninjured leg in patients with ACL deficiency. Test batteries consisting of several hop tests has been described in the previous literature indicating a good test-retest reliability measuring lower leg performance. The functional performance is defined using the limb symmetry index in percent between each individuals lower limbs. This study aims to determine the LSI of healthy subjects using the values achieved by the subjects in the control group. A limb symmetry index (LSI) between 85% and 95% is considered sufficient for return to pivoting sports in patients after knee injury.